2. Indigo (the new comunication layer in Longhorn, actually gonna be released as a seperat install for WinXP and later)

Indigo is the toolset and services to write and
communicate with webservices etc.

Indigo + Avalon is the combination to write the
absolutley coolest applications you can imagine.

3. WinFS, This is the new filesystem on Longhorn. It's actually only a layer on top of the wellknown NTFS (wich also have a lot of new improvements).

WinFS will be the natrual storage for common "things"
such as Contacts, Mail, etc... This way there will allways be a common way to acces your callendar, mail, contacts and this in turn will enable rich applications to integrate seamlessly to this kind of resources.

WinFS also makes it very easy to extend and add new
types of information. I.e. your application might want to add some extra fields of information to the Contcact (Person?) type.